CN104561731B - A kind of production method of poker characteristic uniform high tenacity 65Mn spring steel - Google Patents

Abstract

The invention discloses a production method of high-toughness 65Mn spring steel with uniform cleaning rod performance, belonging to the technical field of spring steel. The specific parameters are: the starting temperature during rolling is 1000°C-1030°C, the temperature at the entrance of the rolling mill is 880°C-900°C after head stripping; the temperature at the entrance of the finish rolling is 830°C-850°C; after the finish rolling, five-stage alternating water cooling is adopted , the silk spinning temperature is 830°C-850°C; during the cooling process of the Steyr mill air cooling line during cooling control, the fan is turned on for quick cooling after spinning, and the insulation cover is started to cool slowly 3m behind the fan, and the overlapping point is placed The cover temperature is 620-630°C, and the cover temperature is 480-500°C. The advantages are that the uniformity of the performance of the 65Mn spring steel is realized, the plasticity and toughness of the wire rod are increased, the drawing yield is improved, and the fatigue performance of the spring steel is improved.

Description

A kind of production method of high-toughness 65Mn spring steel with uniform cleaning rod performance

technical field

The invention belongs to the technical field of spring steel, in particular to a production method of high-toughness 65Mn spring steel with uniform cleaning rod performance. It is suitable for improving the area shrinkage of spring steel wire rod, reducing the performance fluctuation of the same coil of wire rod, and improving the fatigue performance of spring steel.

Background technique

As a very important shock absorption and functional component, spring is widely used in automobile manufacturing and daily life. According to different uses, spring steel is required to have different levels of ductility and fatigue properties. Therefore, different kinds of spring steel were born. The existing spring grades mainly include 65Mn, 60Si ₂ MnA, 55SiCr, etc., which belong to Cr-V series, Cr-Mn series, Si-Mn series, etc., and have the advantages of good hardenability, high strength, and excellent fatigue performance. It is widely used in the production of vehicle springs.

65Mn is a widely used spring steel, mainly used for ordinary spring steel wire, automobile suspension spring, oil quenching-tempering spring steel wire, spring gasket for high-speed rail, etc. It is one of the most important spring steels on the market at present. First, it is also one of the spring steels that are used in large quantities in some areas. Its use is gradually changing from ordinary suspension springs to precision springs, and the amount of drawing is gradually changing to deep drawn products, such as oil quenching-tempering steel wire, which requires the comprehensive mechanical properties of the wire rod to have excellent and uniform cleaning properties. and fatigue fracture resistance.

65Mn spring steel wire rod generally needs cold drawing, surface pickling, heat treatment, coil spring and other processes in the subsequent processing process, which affect the surface quality of the wire rod, the cleanliness of the steel, the central segregation, and the performance of the cleaning rod. Uniformity has strict requirements, otherwise it is easy to cause fatigue fracture, the fatigue resistance is weakened, and the service life of the spring is affected. In severe cases, it is easy to cause serious problems such as wire rod cold drawing fracture, deep drawing fracture, coil spring brittle fracture, etc. Thereby affecting the yield of steel products and reducing the safety performance of materials.

The uniformity of the 65Mn wire rod produced by the existing process is poor, the tensile strength of the same coil fluctuates greatly, and the plastic surface shrinkage of the same coil is seriously uneven, especially the surface shrinkage of the end line is low. Finally, it needs to be placed in the finished product warehouse for more than 1 month before it can be used, otherwise it will break during cold drawing, coil spring and spring washer winding. Therefore, it is necessary to study a new process to improve the uniformity of the steel structure and properties, improve the ductility and toughness of the steel, and reduce the broken wire rate during the cold drawing process.

The application number is CN201210398901.1, the application date is 2012.10.19, and the Chinese patent document titled "a production process of 65Mn spring steel wire rod and 65Mn spring wire rod" discloses a production process route of 65Mn wire rod. The production process of the 65Mn wire rod in this process is mainly to adjust the heating furnace system, solve the problem of improving the depth of the decarburization layer of the 65Mn wire rod, and use the conventional rolling process to obtain a suitable structure and high-strength mechanical properties, but It does not mention the uniformity of the wire rod. From the examples, its tensile strength and area shrinkage fluctuate greatly. With the widespread use of 65Mn purposes, the uniformity of the strip is the main indicator of 65Mn spring steel.

The publication number is CN103484781A, the application date is January 1, 2014, and the Chinese patent document titled "A High-Strength and High-Toughness Spring Steel and Its Manufacturing Method" discloses a high-toughness spring steel, which changes the steel's properties by adjusting the alloy composition. Tensile strength and toughness, but the cost is high, only suitable for special purpose spring steel. Moreover, this patent does not mention the uniform performance of the cleaning rod produced by spring steel, but from the examples, its tensile strength and area shrinkage fluctuate greatly.

The present invention controls the rolling and cooling in the whole process, realizes the austenitization of the billet by controlling the temperature and time of the heating furnace, ensures that the temperature difference between the head and the tail of the billet is less than 30°C, and prevents abnormal grain growth and refines the structure. Coarse and medium rolling, the rolling temperature is controlled in the head-off process, which not only ensures the weldability of high-temperature deformation to defects such as loose shrinkage cavities in the core, but also rolls at the lower limit temperature of the recrystallization range to ensure the deformation of austenite grains. refinement. After the pre-finish rolling, the cooling control measures are continued to realize the low-temperature finish rolling, and the deformation energy can be stored for cooling after rolling to the greatest extent, so as to ensure the refinement of the structure. After rolling, water cooling and low-temperature spinning control the temperature rise of finishing rolling at 80-100°C, so that the temperature of the finishing mill is less than 1000°C, avoiding the temperature range of abnormal growth of the structure, and further shortening the temperature range of the growth of the structure with appropriate cooling. The residence time reduces the growth tendency, realizes the maximum degree of rolling structure refinement, and at the same time weakens the surface stress of the water-cooled wire rod after rolling. The post-rolling air-cooling process adopts the measures of rapid cooling in the dual-phase zone + slow cooling after rolling to ensure that the phase transformation of austenite occurs at an undercooling degree of 100-120°C, and cooperates with the deformation storage energy to induce phase transformation to ensure phase transformation. The interlamellar spacing of the microstructure and the grain size of the final sorbite cluster. Slow cooling after rolling is to reduce the abnormal structure and stress of the core caused by the segregation of 65Mn alloy elements, control its cooling rate in the heat preservation cover, and ensure sufficient slow cooling time for the wire rod above 500°C.

Contents of the invention

The purpose of the present invention is to provide a production method of high-toughness 65Mn spring steel with uniform performance of the cleaning rod, which solves the problems of poor uniformity of the cleaning rod and very large fluctuations in the tensile strength of the same ring. In particular, it provides a method that can reduce the performance fluctuation of 65Mn spring steel in the same ring, reduce the grain size, improve the uniformity of the structure and performance, so as to improve the drawing performance of the finished wire rod and the fatigue performance of the finished spring.

The invention discloses a production method of high toughness 65Mn spring steel with uniform rod performance, which is rolled into a hot-rolled wire rod through the steps of converter smelting, LF furnace refining, continuous casting, heating furnace heating, rolling, controlled cooling and the like. The specific steps and parameters are as follows:

1. Rolling: The starting temperature is 1000°C-1030°C, and the four passes of rough rolling adopt head-off tension-free rolling, and the temperature at the entrance of the rolling mill after head-off is 880°C-900°C; The water tank-recovery section-water tank-recovery section is alternately water-cooled in two sections, and the temperature at the entrance of the finish rolling is 830°C-850°C. The surface of the billet before the finish rolling is bright without obvious black spots. After finishing rolling, the water tank-recovery section-water tank-recovery section five-stage alternate water cooling method is adopted, and the spinning temperature is 830°C-850°C to achieve low-temperature spinning and prevent abnormal grain growth.

2. Controlled cooling: During the cooling process of the Steyr mill air cooling line, turn on the fan for quick cooling after spinning, and start to cover the heat preservation cover for slow cooling at 3m behind the fan. The temperature of the cover is 480-500 ℃; the method of quick cooling in the front section and slow cooling in the back section is adopted to reduce the generation of proeutectoid ferrite, refine the interlamellar spacing of pearlite, and reduce the internal stress of the wire rod.

In step 1, the cooling rate of alternating water cooling after pre-finish rolling and before finish rolling is 30-50°C/s; the water-cooling rate after finish rolling and before spinning is 100°C/s-200°C/s.

The cooling rate of fast cooling in step 2 is 15°C/s-18°C/s; the cooling rate of slow cooling is 2-3°C/s.

The "same circle" mentioned in this article refers to any circle in a coil of wire rod. It is an important indicator reflecting the performance fluctuation of the cleaning rod and a main means of testing the performance of the cleaning rod. The purifier performance in this article is obtained by examining the multi-turn performance.

The advantages of the present invention are:

1) Relying on the existing production line equipment, without changing the existing equipment, the alternate cooling of water cooling box-recovery section-water cooling box-recovery section before finishing rolling and after finishing rolling is used to skillfully achieve the implementation of low temperature rolling Effect;

2) Through low-temperature rolling, low-temperature spinning and controlled Stelmore air-cooling technology to achieve the purpose of refining the original austenite grains and reducing the performance fluctuation of the same ring, so as to achieve the uniformity of the performance of the 65Mn spring steel rod , to increase the plasticity and toughness of the wire rod, improve the drawing yield, and improve the fatigue performance of the spring steel.

Description of drawings

Figure 1 is the 500X microstructure appearance of the cross-section of 65Mn spring steel.

Fig. 2 is the morphology of pearlite lamellar spacing of 65Mn spring steel cross section 10000X.

Figure 3 is the microscopic appearance of the deepest part of the total decarburization layer on one side of the 65Mn spring steel cross-section 200X.

Figure 4 is the grain size morphology of the cross-section 500X of 65Mn spring steel.

detailed description

Example 1:

The billets produced by converter smelting and LF furnace refining and continuous casting are then rolled into hot-rolled wire rods through steps such as heating in a heating furnace, rolling, and controlled cooling. In the rolling process, the rolling start temperature is 1025°C, and the four passes of rough rolling adopt tension-free rolling with head off, and the temperature at the entrance of the rolling mill after head off is 900°C. After the pre-finish rolling and before the finish rolling, the water tank is alternately cooled by water cooling-recovery-water cooling-recovery, and the cooling rate is 50°C/s; the surface of the billet before the finish rolling is bright without obvious black spots. The temperature at the entrance of finish rolling is 845°C. After finish rolling and before silk spinning, five stages of water cooling-recovery control are adopted, and the cooling rate is 100°C/s. In the cooling process, the silk spinning temperature is 830°C. During the cooling process of the Stelmo air-cooled line, the fan is turned on after spinning to reduce the generation of pro-eutectoid ferrite. The heat preservation cover is placed 3m behind the fan for slow cooling. The temperature at the overlapping point is 625°C when entering the hood, and 480°C when leaving the hood. The cooling rate of the wire rod is 15°C/s after spinning and before entering the insulation cover; the cooling rate after entering the cover is 3°C/s, so that the ferrite content in the wire rod structure after cooling is reduced and the pearlite sheet is refined The purpose of spacing and reducing the internal stress of the wire rod.

The test results are as follows: see Table 1 and Table 2 for the tensile strength and area shrinkage of the same ring of 65Mn spring steel φ9mm when it was off the assembly line on the same day and aged for 10 days. The metallographic structure is sorbite + fine flaky pearlite + a very small amount of ferrite, as shown in Figure 1; the lamellar spacing is shown in Figure 2; the total decarburization depth of one side is less than 1%, as shown in Figure 3; The grain size is grade 9.5, as shown in Figure 4.

Table 1 The mechanical properties of the 65Mn spring steel φ9mm in the same coil on the same day

Table 2 Mechanical properties of 65Mn spring steel φ9mm in the same ring on the 10th day of aging

Example 2:

The billets produced by converter smelting and LF furnace refining and continuous casting are then rolled into hot-rolled wire rods through steps such as heating in a heating furnace, rolling, and controlled cooling. In the rolling process, the rolling start temperature is 1005°C, and the four passes of rough rolling are head-off tension-free rolling, and the temperature at the entrance of the rolling mill after head-off is 890°C. After the pre-finish rolling and before the finish rolling, the water tank is alternately cooled by water cooling-recovery-water cooling-recovery, and the cooling rate is 41°C/s; the surface of the billet before the finish rolling is bright without obvious black spots. The temperature at the entrance of finish rolling is 840°C. After finish rolling and before spinning, five stages of water cooling-recovery control are adopted, and the cooling rate is 145°C/s. In the cooling process, the silk spinning temperature is 830°C. During the cooling process of the Stelmo air-cooled line, the fan is turned on after spinning to reduce the generation of pro-eutectoid ferrite. The heat preservation cover is placed 3m behind the fan for slow cooling. The temperature at the overlapping point is 620°C when entering the cover, and 490°C when leaving the cover. The cooling rate of the wire rod is 18°C/s after spinning and before entering the insulation cover; the cooling rate after entering the cover is 2.5°C/s, which reduces the ferrite content in the wire rod structure after cooling and refines the pearlite sheet The purpose of spacing and reducing the internal stress of the wire rod.

Example 3:

The billets produced by converter smelting and LF furnace refining and continuous casting are then rolled into hot-rolled wire rods through steps such as heating in a heating furnace, rolling, and controlled cooling. In the rolling process, the rolling start temperature is 1020°C, and the four passes of rough rolling adopt tension-free rolling with head off, and the temperature at the entrance of the rolling mill after head off is 880°C. After the pre-finish rolling and before the finish rolling, the water tank is alternately cooled by water cooling-recovery-water cooling-recovery, and the cooling rate is 30°C/s; the surface of the billet before the finish rolling is bright without obvious black spots. The entrance temperature of finish rolling is 830°C. After finish rolling and before silk spinning, five-stage water cooling-recovery control is adopted, and the cooling rate is 100°C/s. In the cooling process, the silk spinning temperature is 850°C. During the cooling process of the Stelmo air-cooled line, the fan is turned on after spinning to reduce the generation of pro-eutectoid ferrite. 3m behind the fan starts to cover the insulation cover for slow cooling. The temperature at the overlapping point is 630°C when entering the cover, and 495°C when leaving the cover. The cooling rate of the wire rod is 15°C/s after spinning and before entering the insulation cover; the cooling rate after entering the cover is 3°C/s, so that the ferrite content in the wire rod structure after cooling is reduced and the pearlite sheet is refined The purpose of spacing and reducing the internal stress of the wire rod.

Claims (1)

1. a production method for poker characteristic uniform high tenacity 65Mn spring steel, including converter smelting, LF stove refine, company Casting, heating furnace are heated, roll, are controlled cooling step and be rolled into gren rod, it is characterised in that concrete steps and parameter are as follows:

1) rolling: start rolling temperature is 1000 DEG C-1030 DEG C, roughing four-pass de-head tension free rolling, inlet of rolling mill after de-head Temperature is 880 DEG C-900 DEG C；Cooling by water is replaced by water tank-reply section-water tank-reply section two sections after pre-finish rolling, before finish rolling, Entry temperature at finishing is 830 DEG C-850 DEG C；Water tank-reply section-water tank-reply section five sections is used to replace cooling by water after finish rolling, Laying temperature is 830 DEG C-850 DEG C；

2) cooling is controlled: in steyr mill air-cooled line cooling procedure, open blower fan rapid cooling after weaving silk, start at 3m after blower fan to add a cover Thermal insulation cover slow cooling, overlapped points position enters cover temperature and is 620-630 DEG C, goes out cover temperature 480-500 DEG C；

Step 1) described in pre-finish rolling after, before finish rolling, alternately the rate of cooling of cooling by water is 30-50 DEG C/s；To telling after finish rolling Before silk, cooling by water speed is 100 DEG C/s-200 DEG C/s；

Step 2) described in the rate of cooling of rapid cooling be 15 DEG C/s-18 DEG C/s；The rate of cooling of slow cooling is 2-3 DEG C/s.