Quench Cracking Research Articles

Study of quench cracking of a high carbon and chromium steel bar. (3rd report. Effects of clouding point of polymer quenchant on quench cracking).

The preceding paper has shown that the increase of polyalkylene glycol (PAG) polymer concentration results in a decrease of fin cracks and an increase of vertical cracks, because of the clouding point (81°C) of PAG sol.. This paper deals with the effects of the clouding points of quenchant on the quench cracking of a SUJ 2 bar. The clouding point is affected enormously over pH 13.0 of the PAG quenchant and goes down to 43°C at pH 13.5. The high cooling rate of the PAG quenchant is obtained by the low clouding point quenchant. Therefore, the behavior of quench cracking in the pH 13.5 PAG sol. is similar to that of water. When SUJ 2 was quenched from austenitizing temperature 800°C, a considerable tensile stress existed on the surface area of all specimens, regardless of their pH values. A gel permiation chromatogram shows that the thermostability of PAG quenchant is excellent under sever conditions.

Study of quench cracking of a high carbon and chromium steel bar. 2nd Report. Effects of interrupted quenching and delayed quenching on quench cracking.

The preceding paper has reported that the increase of polyalkylene glycol (PAG) polymer concentration results in the decrease of fin cracks and increase of vertical cracks because of the low cooling rate of the quenchant. This paper deals with the effects of interrupted quenching and delayed quenching on quenching. The residual stress and hardness were measured by the X-Ray diffraction method and Rockwell hardness tester, respectively. The interrupted quenching method is more effective to prevent cracking in PAG solutions. Immersed for 6seconds in 5% PAG sol. and for 15 seconds in 15% PAG sol., the steel bars exhibited high hardness and residual stress. Delayed quenching is less effective to prevent cracking. As the crack percentage decreases, the hardness and residual stress become lower in the delayed quenching.

The distribution of residual stresses of S 55 C quenched by aqueous polymer solutions.

Quench cracking and distortion are generally considered to occur under united thermal and transformational stresses. In this paper quench residual stresses were examined by using a S 55 C steel bar. Various polyalkylene glycol (PAG) solutions and oil were prepared for the quench cooling solutions. The micro structure of the test piece was observed with a metallurgical microscope. The residual stresses caused by quenching were measured by Sachs' method. Considerable tensile and compressive stresses existed on the surface and in the center of the steel. The distribution of stresses and the hardness were related to the PAG content and could be explained clearly by the quench cooling rate.

Study of quench cracking of a high carbon and chromium steel bar. (1st report Effects of austenitizing temperature and properties of polymer quenchant on quench cracking)

Ouench cracking is generally considered to occur under thermal and transformational stresses. In this paper, some of the quench effects on cracks (fin and/or vertical), hardness and residual stresses of a SUJ 2 bar were examined by using polyalkylene glycol (PAG) solutions. The fin crack by water quenching occurred in all specimens at the austenitizing temperatures higher than 800°C. Similarly, the vertical crack occurred in all specimens at higher than 900°C. The increase in PAG polymer concentration results in the decrease of a fin crack and increase of a vertical crack. The PAG quenchant temperature is closely related to the fin crack, because of the clouding points of PAG solutions. The residual stresses caused by quenching were mearured by the X-ray diffraction method. A considerable tensile stress existed on the surface area of all specimens.

中，高炭素低合金鋼のＲＲＣ試験における焼割れの発生挙動 Ｉ 中，高炭素低合金鋼の溶接熱影響部における低温割れの研究

In order to investigate the weld cold cracking of medium, high carbon low alloy steels which is considered to be caused by quench cracking, the fundamental behaviors of this type of cracking were studied by means of the RRC test. Namely, HAZ cracking in JIS SNCM439 (0.4C-1.8Ni-0.8Cr-0.3Mo steel) and JIS SK5 (0.8C plain carbon steel) was studied under the conditions of restraint intensity of about 9.8 to 29.4 kN/mm·mm without preheating utilizing GTA welding with austenitic filler wire to eliminate the effect of diffusible hydrogen. Main conclusions obtained are as follows:(1) General behavior of restraint stress after welding of these steels nearly agrees with that of weldable high strength steels in which martensitic transformation reduces restraint stress.(2) The last stage which gives the maximum or saturated restraint stress after welding is not seen even in the low restraint intensity of about 10 kN/mm.mm, because the cracking develops largely before the last stage.(3) Crack initiation estimated with AE technique occurs earlier with increasing the restraint intensity. The highest temperature of crack initiation, however, was about 35- K and 393 K in SNCM439 and SK5, respectively, meaning fairly lower than their Ms temperatures.(4) The stress at the crack initiation was about 400 MPa and 270 MPa in SNCM439 and SK5, respectively irrespective of the restraint intensity.(5) Crack initiation part has an intimate correlation with liquated grain-boundary in HAZ near fusion boundary, and gives very brittle intergranular fracture surface.

Sulphur segregation and intergranular microcracking in ferritic steel weld metal

Abstract Metallographic and fractographic studies were undertaken to investigate weld metal microcracking in a 2·25Cr–1 M o steel fabrication. Numerous small microcracks were found in single-pass TIG welds in the as-welded condition. An unusual form of brittle fracture on prior austenite grain boundaries was observed, associated with a dense array of intergranular submicrometre sulphide inclusions. The observations indicated that sulphide precipitation had occurred by a solidstate mechanism as the weld metal cooled through the austenite range, while elemental sulphur segregation promoted grain-boundary faceting and embrittlement. The microcracks appeared to have formed on the previously faceted and embrittled grain boundaries by a low-temperature quench cracking mechanism. The factors responsible for the severe sulphur segregation are reviewed, and the implications are discussed in the context of recent interest in the role of grain-boundary sulphides in weld stress relief cracking.

An AES study of temper embrittlement in a low alloy steel

In situ tensile tests were conducted in an Auger spectrometer on specimens of a low alloy steel susceptible to temper embrittlement. The specimens were tested in ultra high vacuum and in a low pressure of high purity hydrogen. Comparisons were made of the stress-strain curves, the fracture modes and the Auger electron spectra obtained from the fracture surfaces. Specimens were tested in the as-quenched martensitic (quenched from 950°C). the unembrittled (tempered at 650°C) and the embrittled (tempered at 500°C) states. Testing in hydrogen changed the mode of fracture, in the asquenched martensitic material, from a normal dimpled rupture to an intergranular, dimpled rupture mode. AES analysis of the intergranular facets showed, with the possible exception of N. no segregation of alloying or embrittling elements. Hydrogen had no major influence on the mode of fracture of samples in the unembrittled or embrittled states. In the temper embrittled material, grain boundary segregation of Sn. P and N together with enhancement of Ni was observed. In all conditions testing in hydrogen had a marked influence in reducing the strain to fracture. Specimens water-quenched from the austenite region were susceptible to intergranular quench cracking. No segregation of impurities was detected on the prior austenite boundaries and it is concluded that the phenomenon of quench cracking is not associated with such segregation.

Design of Fe/4Cr/0.4C martensitic steels eliminating quench cracking

Inter-granular cracking in the as-quenched structures of vacuum melted Fe/4Cr/0.4C steel has been investigated in terms of the heat treatment conditions. It has been shown that amount of carbon in solution and martensite packet size are the two most important factors influencing cracking tendency. Multiple heat-treatments have been designed in order to take advantage of higher austenitizing temperature and fine austenite grain size. Elimination of quench cracking and good mechanical properties were obtained after these treatments.

Segregation Effects and the Toughness of Untempered Low-Alloy Steels

ZACKAY et al.1 have discussed the increase in fracture toughness of untempered ultra-high strength steels resulting from the use of high austenizing temperatures for solution treatment. Their results indicate that the toughness is increased suddenly and dramatically, by a factor of more than two, when the steels are austenized at temperatures greater than 1,100° C (Fig. 1). The effect is promoted by fast quenching rates. They show further that a two-step quenching procedure from high austenizing temperatures (for example, 1,200° C→870° C→quench) can eliminate any danger of quench cracking, whilst causing only a small (7%) reduction in fracture toughness. This improvement in toughness, obtained by using high austenizing temperatures, was attributed to the retardation of grain boundary nucleation of a second phase when high energy grain boundaries, associated with small grains, are eliminated by grain growth.

Effects of water and aqueous solution temperature on quench cracking

1. Tests have confirmed that the heating of water or aqueous solutions increases the sensitivities to cracking of medium-carbon steels quenched to martensite. High-carbon steels are only sensitive to heated water when there is a decarburized surface layer. 2. At the same temperature, aqueous solutions of NaCl and NaOH produce more uniform hardness, and less cracking, than water alone. These solutions may be recommended for cases when cornponents made of carbon steels cannot be quenched by stepped or hot-bath methods. 3. These conclusions relate to components of simple shape and diameters of 5–15 mm.

Steels for surface hardening

1. The considerable technical and economic advantages of surface hardening after high-frequency heating, giving better service performance, labor savings during manufacture, lower heat treating cost and also offering the possibility of complex automation of the production cycle, may be used to fullest extent only if for the components in question a steel is selected whose composition and properties are attuned to the specific features of high-speed induction heating and the kinetics of surface hardening in general. 2. The development of special steels for surface hardening permits uniformity in the quality of the hardened case and suppresses ferrite banding; it also improves the wear resistance and contact strength of the components. 3. Rejects because of quench cracking can be eliminated entirely without the use of soft quenching media which would impair the hardness and service performance of the hardened steel. 4. New steels with reduced hardenability enable wide-spread application of progressive methods of surface hardening to gears and other components having variously shaped zones which must be strengthened.