JPH0262416A - Roll made of heat resistant stainless steel - Google Patents

Abstract

PURPOSE:To hardly generate any fatigue crack caused by thermo-stress by applying heat treatment on the surface side of a cooling water passage on the central axis of a roll so as to remain compression stress, and forming a layer hardened from this passage surface to the depth of about 1-5mm. CONSTITUTION:At first, a high frequency induction heat coil HC with a cooling jacket is arranged on the bottom of a roll center hole 1d while standing the roll 1a. The coil HC is supported by a coil supporting bar GB which is used commonly as a cooling water supply passage and an electric current supply passage so as to secure the clearance between the center hole 1d and the coil HC. Further the inner surface of the hole 1d is hardened continuously by moving this coil HC upward in the center hole 1d while a cooling water (w) spouts at the same time when an electric power supply is operated so as to induction- heat the inner surface of the center hole. After hardened, the inner surface of the center hole 1d is heated to 150 deg.C and tempered spending about 5 hours.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is used for guiding, straightening, drawing, or conveying hot billet or other steel billets, for example, in a continuous casting line of a steelworks. This is related to the role that is used.

[Conventional technology]

Feed rolls used in continuous casting lines, etc., run high-temperature steel pieces such as slabs, blooms, and billets on the rolls. Site-based stainless steel rolls are used.

This roll is provided with boss-shaped shaft parts on both sides of the roll main body formed to an appropriate outer diameter and length, and a central hole that serves as a cooling water passage is provided on the central axis of the roll passing through the shaft part. It is formed by

[Problem to be solved by the invention]

In the above conventional roll, the outer surface of the roll is in contact with the high-temperature steel billet passing through it, while cooling water is supplied to the center hole that serves as the cooling water passage formed in the center of the roll. A temperature difference is generated between the roller and the central hole portion of the roll, and thermal stress is generated.

By the way, when we measured and analyzed the temperature and temperature distribution from the center hole of the roll to the outer surface of the roll when the billet passes through the rolls of currently used billet casting machines, we found the temperature distribution as shown in Figure 5. The thermal stress in the circumferential direction at this time was as shown in the numerical values in FIG.

As can be seen from the temperature distribution and thermal stress values shown in Figures 5 and 6, a tensile stress of approximately 50 kg/am'' is applied to the center of the roll, so conventional rolls have a charge of approximately 3000 after the start of use. When used to an extent.

Fatigue cracks had developed and progressed from the cooling water passage to the inside of the roll, making it unusable.

An object of the present invention is to provide a heat-resistant roll in which fatigue cracks do not or hardly occur due to thermal stress during use.

[Means to solve the problem]

The present invention was made to solve the above problems, and
The structure is such that the cooling water passage that runs through the central axis of the roll is quenched and tempered from the surface side, so that about 50 kg / rrm is applied to the surface side of the cooling water passage.
It is characterized by the fact that a compressive stress of the above level remains and that a hardened layer is formed to a depth of about 1 to 5 wm from the surface of the passage.

[For production]

The compressive residual stress left on the inner surface of the center hole of the roll alleviates the tensile stress caused by thermal stress when a billet or other steel billet passes through the roll, so the compressive stress does not cause cracks on the center hole side.

Further, the hardened layer formed on the surface layer of the center hole increases the yield strength on the side of the center hole of the roll, thereby increasing the fatigue strength.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a vertical cross-sectional view of an example of the roll of the present invention, and FIG.
FIG. 3 is an enlarged partial vertical cross-sectional view conceptually showing an example of a heat treatment mode of the roll shown in the figure.

Therefore, the material of the roll of the present invention shown in FIG.
It is made of 3% Cr martensitic stainless steel, and its shape is such that the outer diameter of the roll body 1a is 350 nmφ,
Its length is 330nw++, the shaft part 1b formed on both sides of this main body 1a and the mounting part IC are 638m, the total length of the roll is 968m5, and the diameter of the center hole 1d formed in the center which becomes the cooling water passage is 40maφ is formed.

Conventionally, rolls of the above material and shape have been tempered on the outer surface of the roll, but after tempering, the inner surface of the center hole 1d, which serves as the cooling water passage, has a hardness of 265 to 280 Hv and a tensile strength. so ~9oicg/m*”, proof stress 60~70 kg
/ mm”, tensile residual stress 5-7 kg/rtva”
There was a time.

In the roll of the present invention, the center hole 1d, which serves as the cooling water passage of the conventional roll, is quenched and tempered.

It has been given certain mechanical properties. Here, in order to confirm the characteristics brought about by the above processing, we will introduce the third
As shown in the figure, the roll is made of the same material as the above roll and has an outer diameter of 160+.
A test piece T with a diameter of sφ and a length of 200 m was made, and a hole 1d' having the same diameter as the center hole 1d of the roll was made through the center of the test piece T, and a quenching and tempering treatment was performed to evaluate the effect of this treatment. I tried measuring it. This process and its effects will be described below.

(Heat treatment method) High frequency power supply: 8 KH-600KVA inverter Hardening method: Internal movement quenching Heating temperature: 1000°C to 1050°C Cooling: Water cooling Tempering conditions = 150°C x 5 hours (Measurement of heat treatment effect) Residual stress measurement: Strain gauge Measuring points: 2 points on the circumference of the hole (0°, 180°), 2 points on the outer circumference (0", 180"), each 40 mm from the end surface
The measurement results of in+ positional residual stress are shown in the following table, and the measurement results of cross-sectional hardness are shown in the chart in FIG.

As can be seen from the above measurement results, a compressive residual stress of about 50 to 70 kg/mm" was obtained on the surface side of the center hole, and a hardened layer was formed by this heat treatment to a depth of about 1 to 5 mm. I was able to confirm that it was done.

Here, the hardness of the inner surface of the test piece T after heat treatment is
As shown in the chart of FIG. 4, since the tensile strength is 500 to 550 Hv, the tensile strength is approximately 170 to 190 kg/+nm'', and therefore the yield strength can be expected to be approximately 130 to 150 kg/mm''.

Generally, the heat treatment applied to the roll of the present invention is carried out by placing the roll shown in FIG. 1 in an upright position, as shown in FIG.

First, a high frequency induction heating coil HC with a cooling jacket is placed at the bottom of the center hole 1d. The coil IC is supported by a coil support bar GB that serves as both a cooling water supply path and a current supply path, and a clearance between the center hole 1d and the coil HC is secured, and when the power is turned on and the inner surface of the center hole is heated by induction. At the same time, the cooling water W is spouted out and this coil H
C moves upward in the center hole 1d, thereby continuously hardening the inner surface of the hole 1d.

After hardening, the inner surface of the center hole 1d is heated to 150° C. and tempered for about 5 hours.

Although the heating means is not limited to high frequency induction heating, high frequency induction heating is preferable in consideration of the fact that the space for quenching is limited.

〔Effect of the invention〕

According to the present invention, by applying the heat treatment applied to the test piece T described above to the center hole 1d, which serves as the cooling water passage of the roll shown in FIG. 1, in the manner shown in FIG. 2, the following effects can be obtained. I was able to get a roll.

The tensile stress generated in the vicinity of the cooling water passage due to thermal stress when a billet or other steel billet passes through is approximately 50 kg/am, but due to the heat treatment, tensile stress of 50 to Since a compressive residual stress of 70 kg/rm" or more is applied, the center hole 1d, which serves as the cooling water passage for the roll, will not crack like in conventional rolls.
It becomes difficult to occur.

In addition, since the roll of the present invention has a hardened layer formed on the inner surface of the center hole through heat treatment, the proof stress value increases, and therefore the fatigue strength also increases significantly, so it does not suffer from fatigue like conventional rolls. The occurrence of cracks due to residual stress can also be significantly suppressed.

In fact, seven rolls of the present invention that had been heat-treated as described in the above example were assembled into a drawing roll of a continuous casting line, and performance was confirmed by comparing them with conventional rolls. However, the roll of the present invention could be used with more than twice the number of charges as the conventional roll, although cracks appeared in the cooling water passage and the roll became unusable.

As described above, the present invention is extremely useful as a roll for guiding, straightening, drawing, or conveying high-temperature steel pieces such as billets.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view of an example of a transport roll, Fig. 2 is an enlarged partial longitudinal cross-section showing an example of the state in which this roll is subjected to heat treatment, Fig. 3 is a perspective view of an example of a test piece, and Fig. 4 is a FIG. 5 is a chart showing the measurement results of the cross-sectional hardness of the test piece, FIG. 5 is a chart showing the temperature distribution of the conventional roll, and FIG. 6 is a chart showing the circumferential direction tensile stress generated in the conventional roll. 1a...Roll body, 1b...Shaft part, 1c...Mounting part, 1d...Cooling water passage, T...Test piece,
Sg...Strain gauge Figure 2

Claims (1)

[Claims] By applying quenching and tempering to the surface of the cooling water passage penetrating the central axis of the roll, a compressive stress of approximately 50 kg/mm^2 or more remains on the surface side of the cooling water passage, and the surface of this passage is A heat-resistant stainless steel roll characterized in that a hardened layer is formed to a depth of about 1 to 5 mm.