Effect of Quenching and Tempering Treatment on the Microstructure and Properties of Q345B Casting

Abstract

This paper mainly discusses the effects of heat treatment of Q345B steel at 900~1060°C quenching +450 tempering treatment on the performance of steel. After heat treatment, the steel °C samples of different treatments were taken to observation and test to get the statistical analysis of test results by changing heat treatment on the properties of the steel. Results show that the quenching treatment enhances the strength and hardness of the steel significantly. After tempering at 450 , the °C plasticity and toughness of steel has also been picked up. The steel has good corrosion resistance when the quenching at 980~1020 . °C Considering the strength, hardness, plasticity and toughness, and the heating temperature, production practice, the heat treatment treatment of quenching at 940 +450 °C °C tempering of steel samples, can make the steel obtain excellent comprehensive properties, which is of great economic significance and practical significance. In recent years, high strength low alloy steel production in our country increases year by year [1], but in the strength, quality, variety series and other aspects there is a gap with foreign advanced level, so it is still a considerable number to import high strength and toughness steel[2-6]. Many foreign researchers already can more accurately predicate and calculate HSLA(high strength low alloy) steel high temperature deformation with microstructure-property prediction method [7-8], and get steel hardened by controlling the morphology of ferrite, even having a better effect than the Peierls-Na-barro strength and solid-solution strengthening[9-10], Japan in terms of earthquake-resistant building steel represents the world advanced level, has developed a series of high-intensity strength 590-1275MPa seismic reinforcement[11].Q345B steel is the largest output and the most widely used high-strength low-alloy steel in our country, Q345B steel-solidified shell plasticity will be low at high temperature, and is prone to produce intergranular cracks under strong cooling intensity and uneven cooling condition[12]. Both domestic and foreign metallurgical workers are unclear to the performance and microstructure changes of continuous casting slab in high temperature treatment [13]. However quenching and tempering can eliminate residual stress inside, steady microstructure, adjust the hardness, strength, plasticity and toughness [14]. According to the performance requirements in different environments, exploring quenching and tempering treatment, fully tapping potential performance of Q345B steel, and obtaining high level-mechanical properties and excellent performance of various materials, is the development trend of new generation of steel materials[15], can greatly enhance the value of materials. 1 Experimental Materials and Method Components of Q345B steel samples tested are: C 0.16, Si 0.36, Mn 1.37, P 0.016, S 0.007, Nb 0.026, the rest is Fe[16], measurement results of the critical point are: Ac1= 770°C, Ac3=917°C, Ms= 400°C[17]. So take 5 samples of 150mm×8mm×7mm and another 5 of 25mm×8mm×7mm at 900, 940, 980, 1020 and 1060°C for insulation, with water as the quenching medium. Set the tempering temperature at 450°C, after tempering take 6 samples of 25mm×8mm×7mm for grinding, polishing and corroded by 4% nitric acid alcohol solution, then observing their microstructure by DMI5000M-metallographic microscope. International Conference on Economy, Management and Education Technology (ICEMET 2015) © 2015. The authors Published by Atlantis Press 385 Take micro-cont 25mm×8m Q345B st Metallogra prepare w= experiment Q345B ste the 6 corro with SPUR plasticity a