REVIEW AND PROSPECT OF HIGH STRENGTH LOW ALLOY TRIP STEEL

Research status of high strength low alloy TRIP (transformation induced plasticity) steels for automobile structural parts is briefly described. Composition and microstruc-ture factors especially the morphology, size and volume fraction of retained austenite, which largely influence the strength and ductility of the steel, are reviewed and discussed one after another. Modelling of the inter-critical annealing and martempering processes as well as the designing of the TRIP steel aided by commercial software are introduced. Some special aspects of the dynamic mechanical properties of TRIP steel are firstly reported.     

低合金高强度钢生产工艺技术的发展

评述近年来国外低合金高强度钢生产工艺技术的发展，我国低合金高强度钢生产工艺技术，的现状和存在的问题，指出工艺技术装备的进步是发展低合金高强度钢品种质量的前提和保证。     

门式刚架结构设计中一些问题的探讨

结合工程设计实践,对门式刚架轻钢结构设计中的钢材选用,结构布置,节约用钢,支撑体系布置,刚架位移限值,高强螺栓选用及构造要求进行探讨。     

控轧控冷工艺对低合金钢显微组织和力学性能的影响

研究了控轧控冷工艺参数中冷却速度和未再结晶区不同压下量对低合金钢的组织和性能的影响。结果表明,当提高未再结晶区的累计压下量时,使钢的晶粒得到细化、强度和韧性有较大提高。轧后冷却速度控制在5-12为宜。     

HSLA-100 steels: Influence of aging heat treatment on microstructure and properties

The structural steels used in critical construction applications have traditionally been heat-treated low-alloy steels. These normalized and/or quenched and tempered steels derive strength from their carbon contents. Carbon is a very efficient and cost-effective element for increasing strength in ferrite-pearlite or tempered martensitic structures, but it is associated with poor notch toughness. Furthermore, it is well known that both the overall weldability and weldment toughness are inversely related to the carbon equivalent values, especially at high carbon contents. The stringent control needed for the welding of these traditional steels is one of the major causes of high fabrication costs. In order to reduce fabrication cost while simultaneously improving the quality of structural steels, a new family of high-strength low-alloy steels with copper additions (HSLA-100) has been developed. The alloy design philosophy of the new steels includes a reduction in the carbon content, which improves toughness and weldability.     

MODELING OF ISOTHERMAL PRECIPrrATION KINETICS IN HSLA STEELS AND ITS APPLICATION

Microalloying elements in high-strength low-alloy steels, such as Nb, Ti and V, precipitate during hot-rolling processes. On the basis of classical theory of nucleation and growth, quantitative modeling of isothermal precipitation was developed, which was tested by the stress relaxation method, the calculated precipitation-time-temperature curve is in good agreements with the measured results, then the model was applied to predict the precipitation behavior during continuous cooling.     

MICROSTRUCTURE AND MECHANICAL PROPERTY DEVELOPMENT IN THE SIMULATED HEAT AFFECTED ZONE OF V TREATED HSLA STEELS

The simulated heat affected zone （HAZ） of the high strength low alloy （HSLA） steels containing 0%, 0.047%, 0.097% and 0.151% vanadium, respectively, were studied with Gleeble-2000 thermomechanical simulator to determine the influence of vanadium addition on the mechanical properties of the HAZ. The HAZ simulation involved reheating the samples to 1350℃, and then cooling to ambient temperature at a cooling rate of 5℃/s ranging from 800 to 500℃ （△8/5=60s）. The mechanical properties including tensile strength and -20℃ impact toughness were conducted. The microstructures of the base steel and the simulated HAZs were investigated using optical microscope, scanning electron microscope （ SEM ） and transmission electron microscope （TEM）. Based on the systemutic examination, the present work confirmed that about 0.05% vanadium addition to low carbon low alloy steels resulted in expected balance of strength and toughness of the HAZ. And more than 0.10% levels addition led to detrimental toughness of the HAZ SEM study showed that the simulated 0.097% and 0.151%V HAZs consisted of more coarse ferrite plates with greater and more M-A constituents along austenite grain and ferrite plate bound- aries. The impact fracture surfaces of the simulated 0.097% and 0.151%V HAZs showed typically brittle mode with predominant cleavages. The size of the facet in the fracture surface increased with increasing vanadium level from 0.097% to 0.151%.As a result, the simulated 0.151% V HAZ has the lowest impact toughness of the four specimens.     

Thermoviscoelastic Behavior in a Circular HSLA Steel Plate

Based on the thermoviscoelastic theory and the classic plate theory, thermoviscoelastic behavior of a circular plate made from high strength low alloy (HSLA) steel material is investigated. Applying the Kirchhoff hypothesis, the nonlinear motion control equations of the circular HSLA steel plate are presented by utilizing the principle of minimum potential energy. The entire problem is solved by utilizing the finite difference method, Newmark method and iterative method. Numerical results show that mechanical loads, boundary conditions, the ratio of thickness to radius, and temperature field have a great influence on thermoviscoelastic behavior of the circular HSLA steel plate.