Intercritical Annealing Treatment Research Articles

Plasticity enhancement and sustainable strain hardening mechanism of a novel developed medium Mn steel

A novel medium manganese steel denoted as Fe-8Mn-0.3C-1.5Si-3Al-0.2Nb (wt.%) is developed via the combination of two-stage warm rolling (TWR) and intercritical annealing (IA), which exhibits excellent strength and elongation of 1203 MPa and 47.2 %, respectively. The sustainable strain hardening and plasticity enhancement in the scenarios of various IA treatments are elaborated via the analysis of TRIP-assisted deformation and fracture mechanisms. It is indicated that the combination of the continuous/discontinuous TRIP effect and the dynamic balance between dislocation pile-ups and annihilation contribute to the sustainable strain hardening. The excellent plasticity is attributed to TRIP effect, plenty of deep/fine dimples and few cracks.

UPAYA PERBAIKAN SIFAT MEKANIK BAJA PLAT JOIN G 3131 SPHC MELALUI SIMULASI PROSES INTERCRITICAL ANNEALING DI INDUSTRI KONSTRUKSI BAJA

Improvement of the mechanical properties of G3131 SPHC equivalent to JIS G 3101 SS330 plate joint steel through intercritical annealing simulations has been carried out. The JIS G 3131 grade SPHC steel was gradually heated by intercritical annealing at temperatures of 750–850 oC for holding times of 1–15 minutes. After intercritical annealing treatment, the tensile strength and yield strength of steel increased compared to non-treatment samples. The average tensile strength obtained was 573 MPa with an increase of 76.85% compared to the tensile strength before the intercritical annealing process. Meanwhile, the yield strength of steel increased by 60% to 421 MPa. Increasing the annealing temperature and holding time will promote the formation of the martensite phase, as well as enlarge the austenite and ferrite grains. Optimal heating variable obtained at a temperature of 750 ℃ with a holding time of 15 minutes. Using these variables produced a tensile strength of 625 MPa and a yield strength of 434 MPa with an elongation of 23% which is standardly included in JIS G 3101 SS400.At the optimal value, the grain growth kinetic of K and n values were 0.280466778 and 0.6905, respectively, with an activation energy (Q) of 12.4268517 J/mol.

Evading the strength-ductility compromise in medium manganese steel by a novel low temperature warm rolling treatment

Strength-ductility trade-off is an enduring problem in a wide range of metals and alloys including the advanced high-strength steels. In this work, we propose a novel non-isothermal low-temperature warm rolling (WR) treatment which was applied after the conventional intercritical annealing (IA) in order to overcome the strength-ductility compromise in a medium manganese steel, Fe-5.1Mn-0.22C-0.85Si-0.42Al (composition in wt%). IA + WR treatment yielded a simultaneous improvement in tensile properties, wherein yield strength (YS), ultimate tensile strength (UTS), and ductility improved by 32%, 12%, and 6% respectively, compared to the conventional IA treatment. Despite an increase in the yield point elongation (2%) and Lüders strain (3%) in the IA + WR specimen, the ductility of the same improved as compared to the IA specimen. Microstructure of the IA + WR specimen was tailored by introducing a significantly higher dislocation density in the constituent ferrite and retained austenite (RA) phases along with a relatively higher density of planar defects (stacking faults and nano-twins) in the RA phase. X-ray line profile analysis quantified the increased dislocation density (order ∼1015 vs 1014 m−2) and twin fault probability (∼1.35% vs ∼0.12%) in the RA phase of the IA + WR compared to the IA specimen. The improvement in YS was primarily due to the increase in the dislocation density of the constituent phases in the IA + WR specimen. Introduction of a high density of lattice defects in the RA phase during the WR treatment above the Md30 temperature enhanced the mechanical stability of the RA phase, leading to a decreased rate of TRIP effect and formation of hierarchical twins during tensile deformation. The near-ubiquitous strength-ductility trade-off was overcome via a tailored microstructure consisting of regulated austenite stability leading to discontinuous TRIP effect, hierarchical twinning in RA phase, and favorable texture in the constituent phases. The present study provides a pathway to tailor the microstructure for escaping the strength-ductility paradox in different metastable FCC alloys such as stainless steel, HEAs, TWIP steels etc.

MECHANICAL BEHAVIOR OF AN HIGH STRENGHT STEEL (AHSS) WITH MEDIUM MN CONTENT IN TWO ROLLING CONDITIONS: HOT AND WARM

The microstructure before intercritical annealing of an AHSS (Advanced High Strength Steel) with medium Mn content plays an important role in the final mechanical properties, since the transformations occurring during annealing modify phases, composition, and morphology. The microstructural changes that occur during intercritical annealing treatment of a medium Mn steel were examined. Two starting material comes from different conditions, hot rolling at 1200°C and warm rolling (initial rolling at 1200°C and subsequent at 680°C). The mechanical properties were related to the transformation phenomena that occur in these steels, mainly TRIP (Transformation Induced Plasticity) and TWIP (Twinning Induced Plasticity) effects. The transformations were verified by SEM (Scanning Electron Microscopy) and X-RD (X-Ray Diffraction). Tensile strength values of 1111 MPa and 17% elongation were obtained by hot rolling route. For the warm rolling route, 35% deformation and a tensile strength of 1357 MPa were obtained. The strain hardening curve was analyzed, showing the presence of the TWIP effect subsequently "saw" behavior related to the discontinuous TRIP effect. The mechanic properties values are related to the difference in morphology phases present. An acicular morphology of a/? (ferrite/austenite) provides a higher value of tensile strength, but low elongation percentage, and a mixture of lamellar and globular morphologies, provides an optimized combination of strength and ductility. Key words: AHSS, medium manganese steel, rolling, heat treatment, discontinuous TRIP effect, TWIP.

Improvement in low-temperature toughness of Fe-6.5Mn-0.08C Medium-Mn steel by multi-step heat treatment

In this study, a novel multi-step heat treatment method, including intercritical annealing and tempering, is proposed to improve the low-temperature toughness of Fe-6.5Mn-0.08C medium-manganese (Mn) steel. The effects of the subsequent tempering treatment on the microstructural evolution and low-temperature toughness of medium-Mn steel were investigated and compared with those of a single intercritical annealing treatment. Medium-Mn steel subjected to intercritical annealing exhibited a duplex microstructure composed of martensite and nanolaminate-retained austenite. The subsequent tempering treatment after intercritical annealing generated a more homogenous distribution of retained austenite, together with an increase in the volume fraction of the retained austenite. The uniformly distributed retained austenite prevented Mn segregation at prior austenite grain boundaries, and the high fraction of retained austenite effectively inhibited crack propagation, leading to an improvement in the low-temperature toughness. In addition, the subsequent tempered medium-Mn steel contained a considerable amount of retained austenite, which could transform into martensite during the impact test, resulting in an impact fracture morphology that changed from cleavage facets to dimples at low temperatures.

Effect of Intercritical Annealing Time on the Microstructure and Mechanical Properties of Dual‐Phase Steel Processed by Large‐Strain Asymmetric Cold‐Rolling

Herein, the effect of intercritical annealing time on the microstructure and mechanical properties of dual‐phase steel processed by large‐strain asymmetric cold‐rolling is studied. It is observed that the martensite islands are uniformly distributed in the ferrite phase in the microstructures of dual‐phase steels due to performing the asymmetric cold‐rolling before intercritical annealing treatment. As the intercritical annealing time increases up to 10 min, the fraction of martensite increases. By increasing the holding time and fraction of martensite, the carbon content of the martensite phase is decreased. The short‐term intercritical annealing eliminates the yield point phenomenon. However, intercritical annealing at 860 °C for 20 min leads to the reoccurrence of a yield point phenomenon. Increasing the intercritical annealing time to 10 min improves the yield strength to 505 MPa and ultimate tensile strength to 834 MPa. However, the strength decreases sharply after the holding time of 20 min. There is a perfect linear relationship between the mechanical properties and the fraction of martensite. Ductile failure is observed at the center of the fracture surfaces of dual‐phase steels while shear failure occurs at the edges of the fracture surfaces.

A low-cost strategy to improve strength-ductility-toughness balance in a low-carbon steel

ABSTRACT The current research introduces a low-cost strategy to improve strength-ductility-toughness balance in low-carbon steel containing 0.08 wt-% carbon by simple heat treatment. As the intercritical annealing temperature increased, the fraction of martensite enhanced. By increasing the annealing temperature from 770 to 830°C, the hardness of dual-phase steel was increased from 183 HV to 212 HV, which was due to the increment of martensite fraction from 0.28 to 0.49. The strength of all dual-phase steel samples produced by intercritical annealing treatment was higher than that of the initial sample owing to the presence of hard martensite in the soft ferrite. The interesting point was that the ductility of the dual-phase steels was almost the same as the initial sample. This led to a remarkable increase in the toughness of dual-phase steels compared to the initial sample. All dual-phase steels revealed a perfect ductile fracture.

Improvement of tensile properties of low-carbon steels via short-time intercritical annealing

The effect of low volume fraction formation of martensite on the tensile properties of low carbon steel was evaluated. First, steel samples with ferrite-cementite microstructure were produced. The thermomechanical treatment used included austenitizing at 1000 °C and then quenching in ice brine solution, tempering the obtained martensitic structure for 1 h at 650 °C, 80% cold rolling, and re-tempering for 2 h at 650 °C. In order to form a low volume fraction of martensite, steel samples with ferrite-cementite microstructure were intercritically annealed for 30 seconds at 740 °C. As a result of intercritical annealing treatment, 6.2% martensite was formed. The results of tensile test showed that the formation of 6.2% martensite led to the elimination of yield point phenomenon and Lüders banding, decrease of yield stress and increase of true stress at maximum load, while true uniform strain did not change significantly. The work hardening rate also increased significantly. Based on the results of modeling of the flow behavior with the Holloman equation, the work hardening capability of the steel sample including ferrite-cementite decreased after a certain plastic strain, while the work hardening capacity remained constant with the formation of a low volume fraction of martensite in the microstructure.

Time-Dependent Evolution of Volume Fraction and Stability of Retained Austenite in a Hot-Rolled and Intercritically Annealed Al-Alloyed Medium-Mn Steel

The development of superior mechanical properties in medium-Mn requires the optimization of microstructural parameters such as retained austenite (RA) stability, volume fraction, and morphology. The present work explores the possibility of using a continuous annealing approach instead of conventional batch annealing to perform an intercritical annealing (IA) treatment in a hot-rolled strip of an Al-alloyed 5Mn steel. Dilatometric studies were performed at a temperature of 680 ºC with soaking times ranging from 1 to 300 min to follow the microstructural changes as a function of time. The microstructures thus obtained were thoroughly characterized by means of X-ray diffraction, SEM and TEM, TEM-EDS microanalysis and EBSD phase and orientation maps. It was observed that with increasing soaking times, the volume fraction of retained austenite gradually increases, albeit at the cost of its stability. The comparison of martensite start temperatures (Ms) based on the chemical composition of austenite at 680 ºC with that experimentally obtained at higher process temperature revealed the effect of the grain size on the reduction of RA stability for longer process times. Accordingly, mechanical tests results showed that the yield stress, tensile strength and hardness decrease with an increase in the IA soaking time.

Tuning strength-ductility combination of AISI 1008 steel through large strain single-roll drive rolling and intercritical annealing

In this study, the influence of large-strain single-roll drive rolling and intercritical annealing on the microstructure evolution and mechanical behavior of AISI 1008 steel was investigated. The microstructures of all fabricated dual-phase (DP) steels exhibited equiaxed and homogeneously distributed fine ferrite grains and martensite islands. Compared to the as-received sample, the hardness of the produced dual-phase steels increased by up to 100%. As the temperature of intercritical annealing treatment increased, the hardness of the dual-phase samples increased from 233.2 HV to 258.4 HV. All fabricated DP steels showed much higher strength and toughness than the as-received sample. Overall, with increasing the temperature of intercritical annealing, the strength, ductility, and toughness of DP steels were improved due to increasing the martensite fraction. Also, by increasing the temperature of intercritical annealing from 770 to 860°C, the work hardening rate of the DP sample was enhanced. The hardness and strength of dual-phase steels had a good linear correlation to the fraction of martensite. The failure mechanism of the 80% rolled sample was mainly brittle while all DP samples exhibited a perfect ductile fracture characterized by many homogeneous deep dimples without any cleavage facets.

On the Formability of Medium Mn Steel Treated with Varied Thermal Processing Routes

In this contribution, we investigate the influence of thermal processing routes on the formability of medium Mn steel by assessing the strain hardening coefficient and anisotropy factor using the uniaxial tensile test. Medium Mn steel processed by intercritical annealing (IA) at 680 °C for 4 h demonstrates better formability than steel treated with a combination of IA at 800 °C for 10 min and quenching and partitioning (Q&P), based on the much higher strain hardening coefficient (n) and comparable anisotropy factor (r, rm, ∆r). The higher strain hardening coefficient of medium Mn steel with single IA treatment is ascribed to the enhanced transformation-induced plasticity (TRIP) effect resulting from the large amount of austenite that is transformed into martensite during deformation. In addition, the IA process allows for the production of medium Mn steel with high ductility, which is beneficial for its high formability and good 'part ductility' in lightweight automotive applications.

Effect of Intercritical Temperature on the Microstructure and Mechanical Properties of a Ferritic-Martensitic Dual-Phase Low-Alloy Steel with Varying Nickel Content.

Dual-phase low-alloy steels combine a soft ferrite phase with a hard martensite phase to create desirable properties in terms of strength and ductility. Nickel additions to dual-phase low-alloy steels can increase the yield strength further and lower the transformation temperatures, allowing for microstructure refining. Determining the correct intercritical annealing temperature as a function of nickel content is paramount, as it defines the microstructure ratio between ferrite and martensite. Likewise, quantifying the influence of nickel on the intercritical temperature and its synergistic effect with the microstructure ratio on mechanical properties is vital to designing dual-phase steels suitable for corrosive oil and gas services as well as hydrogen transport and storage applications. In this work, we used a microstructural design to develop intercritical annealing heat treatments to obtain dual-phase ferritic-martensitic low-alloy steels. The intercritical annealing and tempering temperatures and times were targeted to achieve three different martensite volume fractions as a function of nickel content, with a nominal content varying between 0, 1, and 3-wt% Ni. Mechanical properties were characterized using tensile testing and microhardness measurements. Additionally, the microstructure was studied using scanning electron microscopy coupled with electron backscatter diffraction analysis. Tensile strength increased with increasing martensite ratio and nickel content, with a further grain refinement effect found in the 3-wt% Ni steel. The optimal heat treatment parameters for oil and gas and hydrogen transport applications are discussed.

Strain rate response of mechanical behaviors for Fe-8Mn-6Al-0.4C duplex low-density steels with different austenite stabilities

Duplex low-density steels exhibit excellent mechanical properties under quasi-static tensile tests with the help of the transformation-induced plastic (TRIP) effect produced by the deformation-induced martensitic transformation (DIMT), which is sensitive to the strain rate. Therefore, adjusting the microstructure to accommodate the deformation at different strain rates is crucial for the optimal design of high-performance duplex low-density steels. In this study, Fe-8Mn-6Al-0.4C low-density steel was subjected to intercritical annealing (IA) treatment to obtain duplex microstructures with an inhomogeneous distribution of austenite grain sizes and tensile tests were performed at two strain rates. The response of the mechanical behavior to the strain rate was investigated, and the mechanical stability of austenite was evaluated using a method based on the grain size. The results show that the diverse mechanical behaviors of experimental steel depend mainly on the mechanical stability of austenite rather than the stacking fault energy (SFE). The mechanical stability of austenite increased with decreasing annealing temperature and was further enhanced by adiabatic heating at a higher strain rate. Accordingly, the DIMT mode changed from a stress-induced transformation to a strain-induced transformation until the DIMT was inhibited by adiabatic heating. The improvement in the mechanical properties of the experimental steel is attributed to the sustainable DIMT with a reasonable mechanical stability of austenite.

Microstructure evolution and yield strength improvement of a low carbon medium manganese steel experienced intercritical annealing, pre-straining and tempering

The microstructure evolution and mechanical properties of a 0.15C1.2Si10Mn0.5 V medium manganese steel after intercritical annealing, pre-straining and tempering treatment are systematically analyzed. An intercritical annealing yields a microstructure containing ultrafine γ + α coexisting structure while final tempering reduces martensitic supersaturation, which is beneficial to the ductility of the steel. The applied pre-strains between the two processes cause a part of unstable banded austenite in hot rolled state prematurely to transform into lath martensite that divides the coarse banded austenite into smaller ones. When the pre-strain is 0.02, there are about 21% strain-induced martensite produced in the microstructure and the steel exhibits the best comprehensive mechanical properties with the yield strength of 1264 MPa, tensile strength of 1506 MPa and total elongation of 19%. Actually, the increase in yield strength under pre-strains should be ascribed to dislocation strengthening in the strain-induced martensite and the precipitation strengthening of vanadium carbides during the deformation and subsequent tempering.

Intercritical annealing treatment of PHS2000 and study of its microstructure and properties

Dual-phase steel (also known as DP steel) is the most widely used ultra-high-strength steel in automobile covering parts and structural parts. Since the concept of automotive lightweight has been put forward and deepened, the development of higher strength grade DP steel and the study of its microstructure and properties are of great significance. In this paper, the Gleeble-3800 thermal simulation machine was used to investigate the phase transition characteristics of the PHS2000. Scanning electron microscopy (SEM) was used to study the evolution of the microstructure under different heat treatment conditions, and the mechanical properties of dual phase microstructure under different conditions were analyzed. The results show that the microstructure of PHS2000 remains martensite with a high volume fraction after intercritical annealing and becomes full martensite after a long time of holding. At the same time, the tensile strength increases, and the plasticity decreases with the increase of the intercritical annealing temperature.

Correlation between microstructure and shape memory properties in an Fe-9.5Ni-6.5Mn dual phase steel developed by intercritical annealing and subsequent ageing

Research was conducted to investigate the shape memory properties related to the microstructure in an Fe-9.5Ni-6.5Mn (wt.%) dual phase steel developed by intercritical annealing and subsequent ageing. Electron back scattering diffraction (EBSD) analysis and high resolution transmission electron microscope (HRTEM) images revealed that the microstructure of the initial steel in the solution-annealed condition was a typical lath α′-martensite with a high density of dislocations. During the intercritical annealing treatment of the solution-annealed steel at 590 °C in the ferritic-austenitic (α+γ) two-phase region for various annealing times, a part of α′-martensite transformed to the reversed γ-austenite with a difusionless shear nature, resulting in the development of a dual-phase (α′+γ) steel. Also, subsequent ageing treatment of the intercritically annealed steel at 480 °C for 3.6 ks led to formation of the nanoscale θ-NiMn precipitates in the dual-phase microstructure. The experimental results indicated a maximum shape recovery of ∼55% at 1% pre-strain for the intercritically annealed steel for 1.8 ks, followed by subsequent ageing. The presence of austenite phase reinforced by precipitates in the dual-phase steel was the main reason for appearance the shape recovery. In addition, the existence of isolated stacking faults in the reversed austenite region after straining confirmed that the occurrence of the austenite to ε-martensite transformation (γ→ε) under loading and the reverse transformation (ε→γ) upon heating are the main causes of the shape memory effect in the studied steel.

An alternative quenching and partitioning (Q&P) process via spheroidization

A hot-rolled Fe-CMnSiMo alloy was subjected to quenching followed by a spheroidization treatment, which resulted in a microstructure consisting of Mn enriched cementite particles dispersed in the ferrite matrix. The as hot-rolled and spheroidized material was subjected to short-duration intercritical annealing (IA) treatment followed by the full quenching and Q&P treatments. The IA treatment was such that the austenite formed as a result of dissolution of cementite particles retains its higher Mn content. The influence of this chemical inhomogeneity on martensite transformation and retained austenite stability was investigated using a dilatometer and interrupted compression experiments, respectively. The results were compared with the microstructure obtained in the absence of chemical heterogeneity by subjecting the hot-rolled material to similar heat treatment directly without the quenching and spheroidization treatment. After the IA treatment, the Ms temperature of the spheroidized material was 36 °C higher than the Ms temperature of the as hot-rolled material. Nevertheless, a higher fraction of retained austenite was stabilized in the spheroidized material after the IA treatment followed by full quenching. The SEM, TEM and DICTRA modelling results showed that cementite particles dissolve during the IA treatment of the spheroidized material and the product austenite retains its higher Mn content. Interrupted compression test results show that the retained austenite in the spheroidized material has greater stability because of its higher Mn content and small size.

Effect of intercritical annealing and subsequent ageing on the microstructure and mechanical properties of a medium Ni–Mn low carbon steel

The aim of this research was to develop a medium Ni–Mn dual phase steel with a combination of relatively high strength and good formability for industrial applications. Accordingly, this research was conducted to examine the effects of intercritical annealing and subsequent ageing treatments on the microstructure and mechanical properties of an Fe-9.5Ni-6.5Mn (wt.%) low carbon martensitic steel. Electron back scattering diffraction (EBSD) analysis revealed that intercritical annealing treatment at 610 °C in the ferrite + austenite (α+γ) dual phase region for various holding times led to formation of the reversed austenite phase in the martensite matrix, producing a medium Ni–Mn dual phase steel. It was resulted that the volume fraction of austenite and its grain size were significantly increased with increasing the holding time. Also, high resolution transmission electron microscope (HRTEM) images illustrated the formation of nano-sized θ-NiMn precipitates within the martensite phase after subsequent ageing at 450 °C for 7.2 ks. Intercritical annealing followed by ageing yielded a good combination of an ultimate tensile strength (∼1160 MPa) and fracture strain (∼11.5%) in the developed dual phase steel compared to the initial martensitic steel. The high strength and good ductility of the developed dual phase steel were respectively attributed to the presence of θ-NiMn precipitates with a hard character and reversely formed austenite with a ductile nature in the microstructure. Furthermore, the fully brittle fracture mode in the aged initial steel changed to a mixture of brittle and ductile behavior in the dual phase steel produced by intercritical annealing and subsequent ageing.

Effect of partitioning treatment on the microstructure and properties of low-carbon ferritic stainless steel treated by a quenching and partitioning process

We carried out a quenching and partitioning (Q&P) process to some samples of AISI 430 ferritic stainless steel and applied intercritical annealing treatment to others as a comparison. The microstructure of the sample after intercritical annealing treatment contained ferrite and martensite. The microstructure of samples under the Q&P process included ferrite, martensite, and retained austenite. The strength of samples treated by a Q&P process was equivalent to that of the samples after intercritical annealing treatment. The former had better ductility than the latter through optimizing the partitioning process parameters. As the partitioning temperature increased, the diffusion rate of carbon atoms increased, more carbon atoms diffused from martensite into austenite, and more retained austenite stabilized at room temperature. The area fraction change of retained austenite resulted from the competitive mechanism of diffusion and homogenization of carbon in austenite and austenite decomposition. The partitioning process had no apparent effect on the strength but significantly affected ductility. The influence of the TRIP effect of retained austenite and softening effect of martensite on ductility should be considered comprehensively. The TRIP effect mainly depended on the fraction and mechanical stability of retained austenite. The diffusion process of carbon atoms during the partitioning stage was briefly described. Part of carbon atoms diffused from martensite into austenite, part of carbon atoms formed precipitation, and part of carbon atoms was trapped by defects at grain boundaries. The relationship between the yield platform and the Cottrell atmosphere formed by carbon pinning dislocation was illustrated in this paper.

Effects of CGL-compatible thermal processing, starting microstructure, and Sn micro-alloying on the mechanical properties of a medium-Mn third generation advanced high strength steel

Two prototype medium-Mn third generation advanced high strength steels (Fe-0.2C-6Mn-1.5Si-0.5Al-0.5Cr-xSn wt%, x = 0 or 0.05) were annealed with continuous galvanizing line (CGL) compatible thermal processing parameters. It was found that the starting microstructure, intercritical annealing (IA) parameters and Sn micro-alloying had a significant effect on the volume fraction, stability, and deformation-induced transformation kinetics of the retained austenite and, therefore, the resultant mechanical properties of the steels. It was shown that Sn segregation at the carbide/matrix interface inhibited C diffusion and consequently, reduced carbide dissolution and precipitation kinetics during intercritical annealing. This resulted in lower volume fraction of retained austenite with lower stability after intercritical annealing of the as-received cold-rolled Sn-containing alloy. CGL-compatible IA treatments, therefore, were only able to produce target 3G-AHSS mechanical properties in the as-received cold-rolled alloy without Sn micro-alloying. However, the martensitic starting microstructures were more robust in achieving the 3G-AHSS target mechanical properties for both alloys. A martensitic starting microstructure resulted in higher volume fraction of stable retained austenite for 650 °C and 675 °C IA treatments. Gradual transformation of this stable retained austenite to martensite (TRIP effect) and mechanical twinning (TWIP effect) resulted in high sustained work hardening rates during plastic deformation. As a result, a favourable strength/ductility balance was achieved in the prototype steels. Moreover, Sn micro-alloying did not have a significant detrimental effect on the mechanical properties for the martensitic starting microstructure heat treatments which achieved target 3G-AHSS properties. This is promising in terms of developing a CGL-compatible processing route for these prototype steels.