1、45——优质碳素结构钢，是最常用中碳调质钢
1, 45 - quality carbon structural steel is the most commonly used medium carbon quenched and tempered steel.
主要特征: 最常用中碳调质钢，综合力学性能良好，淬透性低，水淬时易生裂纹。小型件宜采用调质处理，大型件宜采用正火处理。应用举例: 主要用于制造强度高的运动件，如透平机叶轮、压缩机活塞。轴、齿轮、齿条、蜗杆等。焊接件注意焊前预热，焊后消除应力退火。
Main features: the most commonly used medium carbon quenched and tempered steel, good comprehensive mechanical properties, low hardenability, easy to crack when water quenching. Small parts should be treated with quenching and tempering, and large parts should be treated with normalizing. Examples are mainly used for manufacturing high strength moving parts, such as turbine impeller and compressor piston. Shaft, gear, rack, worm and so on. The welds should be preheated before welding, and stress relieving after welding.
2、Q235A（A3钢）——最常用的碳素结构钢
2, Q235A (A3 steel) - the most commonly used carbon structural steel.
主要特征: 具有高的塑性、韧性和焊接性能、冷冲压性能，以及一定的强度、好的冷弯性能。应用举例: 广泛用于一般要求的零件和焊接结构。如受力不大的拉杆、连杆、销、轴、螺钉、螺母、套圈、支架、机座、建筑结构、桥梁等。
Main features: high plasticity, toughness and weldability, cold stamping performance, as well as a certain strength, good cold bending performance. Application examples: widely used in general requirements of parts and welding structure. For example, tension rod, connecting rod, pin, shaft, screw, nut, ring, bracket, frame, building structure, bridge, etc.
3、40Cr——使用最广泛的钢种之一，属合金结构钢
3. 40Cr, one of the most widely used steels, belongs to alloy structural steel.
主要特征: 经调质处理后，具有良好的综合力学性能、低温冲击韧度及低的缺口敏感性，淬透性良好，油冷时可得到较高的疲劳强度，水冷时复杂形状的零件易产生裂纹，冷弯塑性中等，回火或调质后切削加工性好，但焊接性不好，易产生裂纹，焊前应预热到100～150℃，一般在调质状态下使用，还可以进行碳氮共渗和高频表面淬火处理。
Main features: After quenching and tempering, it has good comprehensive mechanical properties, low-temperature impact toughness and low notch sensitivity, good hardenability, high fatigue strength when oil-cooled, easy to crack when water-cooled parts with complex shape, moderate cold-bending plasticity, good machinability after tempering or tempering, but not weldability. Good, easy to crack, before welding should be preheated to 100 ~ 150 degrees C, generally used in quenching and tempering state, but also for carbonitriding and high-frequency surface quenching treatment.
应用举例:调质处理后用于制造中 速、中载的零件，如机床齿轮、轴、蜗杆、花键轴、顶针套等，调质并高频表面淬火后用于制造表面高硬度、耐磨的零件，如齿轮、轴、主轴、曲轴、心轴、套筒、销子、连杆、螺钉螺母、进气阀等，经淬火及中温回火后用于制造重载、中速冲击的零件，如油泵转子、滑块、齿轮、主轴、套环等，经淬火及低温回火后用于制造重载、低冲击、耐磨的零件，如蜗杆、主轴、轴、套环等，碳氮共渗处即后制造尺寸较大、低温冲击韧度较高的传动零件，如轴、齿轮等。
Examples of applications: quenched and tempered parts for medium speed and medium load, such as machine tool gears, shafts, worms, spline shafts, thimble sleeves, etc., quenched and tempered and quenched at high frequencies for high hardness and wear-resistant parts such as gears, shafts, spindles, crankshafts, mandrels, sleeves, pins, connecting rods, screws and nuts, air intake Valves, after quenching and tempering, are used to manufacture heavy-duty, medium-speed impact parts, such as oil pump rotor, slider, gear, spindle, sleeve ring, etc. After quenching and tempering at low temperature, they are used to manufacture heavy-duty, low impact, wear-resistant parts, such as worm, spindle, shaft, sleeve ring and so on. Carbonitriding is a large size after manufacturing. Low temperature impact toughness parts such as shafts and gears.